Recent reports suggest that commercial-grade valves have now reached the same degree of quality and reliability as nuclear-grade valves. Practically speaking, these reports imply it is safe for highly demanding facilities, such as nuclear plants, to replace their highly specific, purpose-made valves with serially produced conventional ones.
Why would a facility want to replace its specialized valves with alternative ones? One big reason would be to save costs. Yet never, ever at the expense of safety, which is at the very core of nuclear power production.
This blog is a summary of a recent master’s thesis done in collaboration with Metso to investigate just that – the viability of replacing nuclear-grade valves with commercial-grade ones in the Nuclear Safety Class 3 (SC3).
Emergency shutdown valves: challenges and requirements
For this study, performance and safety requirements for the more expensive nuclear-grade on-off shutdown valves in SC3 were compared with the requirements for a similar class of valve, such as Emergency Shutdown (ESD) valves, used in the fuel and petrochemical industries.
Typical challenges for fuel and oil ESD valves include:
- Tight shutoff
- Erosive, corrosive, sticky and toxic fluids
- Strict quality and emission requirements
- Fire safety
- Partial stroke testing during normal operation
- Safety factors for valve and actuator sizing
- Outstanding durability and reliability
Highest safety rating, regardless of application
Metso’s valves for ESD applications in fuel and petrochemical plants include many proven high-quality solutions, each with unique and well-proven safety features. But are they suitable for the challenges of nuclear applications?
For example, Metso’s Neldisc is a high-performance butterfly valve, providing close to equal-percentage characteristics and superior tightness – exactly what is required in nuclear use. The X Series valves are especially suited for highly demanding low-pressure services.
Metso’s Neles ValvGuard is another product of note when it comes to safety. A top-class intelligent safety solenoid, ValvGuard offers partial stroke testing and other diagnostics data. It is engineered specifically to ensure safe and reliable ESD valve operation, relevant for both petrochemical and nuclear plants.
More study needed
According to the research findings of this thesis, most safety requirements for nuclear on-off valves and equivalent oil and gas valves are similar. Yet, specific nuclear conditions are required for sufficient proof that a commercial-grade component is able to perform its safety function in those environments.
Certain nuclear-specific needs, such as radiation tolerability, demand different valve materials than conventional processes. However, these cases do not cover all SC 3 components. To ensure the production of reliable and competitive nuclear power in the future, we must find a way for commercial-grade valves to get accepted for use in nuclear-specific conditions, when they meet identical specifications.
This study provides a good basis for kicking off a discussion on saving costs when it comes to replacing expensive nuclear-grade valves with cost-efficient, safe and equally reliable alternatives. Another benefit of this study is to open new channels of discussion between representatives of nuclear and other industries. This leads to sharing the best practices in each industry. It also helps to learn about the different acceptance methods used to reach the same level of safety in one’s own plant operation – whether it’s a chemical or a nuclear power plant.
This study and collaboration were very important first steps towards increasing our knowledge on this topic, but there is a lot to do before the use of commercial-grade valves in nuclear power plants becomes mainstream.
If you have any questions relating to this thesis or Metso’s valve solutions, or you wish to continue discussing the more technical topics presented here, please contact the author or product managers mentioned below.
Read the complete research study at this Tampere University of Technology web address.
Oskari Raitanen, Master’s thesis author, Energy and Biorefining Engineering graduate student, Tampere University of Technology
Mikko Tikka, Metso contact for the case study, Product Manager, Neles Control Valves
Valtteri Koskinen, Product Manager, Neles Ball Valves
Petri Ilonen, Product Manager, Neles L-series Butterfly Valves
Ville Kähkönen, Director, Industry Management and Marketing
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Technical Sales Engineer, Metso Flow Control